Engine systems include an aftertreatment system to convert the engine exhaust into clean engine exhaust before it is routed to the atmosphere. The aftertreatment system includes a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF). The DOC may include a honeycomb structure coated with a platinum group catalyst. The DOC is provided to oxidize carbon monoxide, unburned hydrocarbons, and the soluble organic fraction (SOF) of diesel particulates to CO2 and H2O. Further, the DPF is used to trap the particulate matter (PM) or soot produced by diesel engines. The aftertreatment system may also include a selective catalytic reduction (SCR) device also having a catalyst washcoat, and the catalyst washcoat is located downstream of a reductant injector. A gaseous or liquid reductant is sprayed or injected into the engine exhaust upstream of the catalyst washcoat by the reductant injector. As the reductant is absorbed by the catalyst washcoat, the reductant reacts with NOx (mainly NO and NO2) present in the engine exhaust to form water (H2O) and elemental nitrogen (N2).
The aftertreatment system usually operates at high temperature and is also required to be maintained at the high temperature to achieve an optimal conversion efficiency of the aftertreatment system. For example when an engine starts in cold weather, it is desired to immediately increase the temperature of the aftertreatment system to a certain level, for example, above 300 degrees Celsius, to ensure the optimal conversion efficiency during the engine start-up. In addition, in cold operating conditions whenever there is a hot shutdown of engine system, the aftertreatment system may experience air-to-air thermal shocks. For example, the temperature inside the aftertreatment system may be as high as 600 degrees Celsius when the outside ambient air temperature is about negative 25 degrees Celsius. There is a high temperature gradient across a housing of aftertreatment and thus heat flux across the aftertreatment housing is large. Such thermal shocks accelerate the aging process of the aftertreatment system and reduce its useful life.
U.S. Pat. No. 8,056,320 discloses a cold-start control system including an air pump control module that controls an air pump and an engine starting module that starts an engine. The air pump control module activates the air pump to supply oxygen to a catalytic converter based on a temperature of the catalytic converter. The engine starting module starts the engine based on the temperature of the catalytic converter. However, the disclosed cold-start control system does not solve the problem related to the hot shutdown of the engine, and the aftertreatment system may experience the air-to-air thermal shocks.